A multiple-input multiple-output (MIMO) technology is an important means to improve a channel capacity of a wireless communications system. In an ideal situation, a capacity of a system including Nt transmit antennas and Nr receive antennas may be approximately improved by Nt×Nr times. Any receive antenna instantly receives a superposed signal from the Nt transmit antennas. Each receive antenna needs to estimate channel information of each transmit antenna according to the superposed signal. Before estimating the channel information of each transmit antenna, the receive antenna first needs to identify different transmit antenna ports, where the different transmit antenna ports use different reference signals (RSs), and the receive antenna mainly identifies the transmit antenna ports by using the reference signals.
In a Long Term Evolution (LTE) system, transmit antenna ports are differentiated by using a method of time-frequency orthogonality, that is, for different transmit antennas, RSs are inserted at different time points and frequencies. FIG. 1 is a mapping (mapping) of reference signals when an LTE system uses four transmit antennas. As shown in FIG. 1, the mapping of the reference signals is a two-dimensional mapping, and includes two dimensions: time and frequency dimensions. Four transmit antennas exist at a transmit end, and are separately an antenna 0, an antenna 1, an antenna 2, and an antenna 3. T0 represents a time-frequency point at which the antenna 0 inserts a reference signal, T1 represents a time-frequency point at which the antenna 1 inserts a reference signal, T2 represents a time-frequency point at which the antenna 2 inserts a reference signal, T3 represents a time-frequency point at which the antenna 3 inserts a reference signal, and time-frequency points other than the time-frequency points at which the reference signals are inserted are time-frequency points at which user data is inserted. As can be shown from FIG. 1, the time-frequency points at which the antennas send the reference signals are different from each other, so that the different transmit antennas can be differentiated according to the time-frequency points, but the reference signals sent by the antennas are the same.
Time-frequency resources occupied in sending reference signals increase in direct proportion as a quantity of MIMO transmit antennas increases. A time-frequency resource allocated to a transmit antenna for sending a reference signal cannot be used by another antenna, which can cause a waste of time-frequency resources, and reduce spectral efficiency and a throughput of the entire system.